# Particle in Expanded 1D Box

## Homework Statement

A particle was originally in a 1D potential box of length L and in its ground state. However, the walls of the box expanded symmetrically to 2L suddenly. Calculate the probability of the particle remaining in its ground state.

## Homework Equations

$$\psi$$(x) = $$\sqrt{\frac{2}{L}}$$ sin ($$\frac{n\pi x}{L}$$)

## The Attempt at a Solution

When I checked https://www.physicsforums.com/showthread.php?t=68816", the answer seems to be (8/3pi)^2... Can anyone guide me as to what is wrong with my working?